There are two basic prior-art techniques of picturing and/or studying different parts of the eye, such as the retina, especially for medicinal purposes.
The first technique is still photography, which is carried out by means of a flashlight emitting white light. This still can be obtained in color thanks to the light emitted by the flashlight being white. By using this technique it is not possible to continuously follow sequences and changes since you are dependent on the charging time of the flashlight.
The second technique is filming, in real time, using infrared light. The reason for using infrared light is that the pupil does not become smaller. Thus, sufficient light intensity for filming is achieved. With infrared light, only the differences in heat or temperature in the pictured object are measured. The drawback of this technique is that the detailed information disappears since there is no difference in heat between small details in the object.
Filming makes it possible to continuously follow sequences and changes. Besides recording a sequence for later analysis, it is of course also possible to observe the sequence as it proceeds.
There is one drawback, however, viz. only such parts of the eye as reflect precisely the incident infrared wavelengths can be seen by using the prior-art technique. This means that all the other information from other parts of the color spectrum is not available.
An example of a similar technique is disclosed in European Patent Application EP 554 643. The light illuminating the eye has a predetermined wavelength and can be produced by a light-emitting diode. A light amplifier amplifies the light reflected in the eye, whereupon a CCD TV camera performs the conversion to a picture, which then constitutes a monochromatic reproduction.